Carrier route record

WNDEN→SLC

Southwest Airlines · Denver to Salt Lake City

Flights: 2,329
Period: July 2025 to June 2026
Share of route: 30%
Carriers: 5

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.

Southwest on DEN to SLC sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 6 points worse than the national rate of 77.6%. The late ones land roughly 50 minutes behind schedule. That rests on 2,329 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 1,689 at 82.3% on time.

Delta Air Lines is the most reliable of the four carriers covered here at 82.3% on time across 1,689 flights.

On time

71.2%

Arrivals under 15 minutes late, of 2,316 completed flights

Avg delay

52 min

Across delayed arrivals only, not all flights

Cancelled

0.47%

National rate is 1.81%

Whole route

77.5%

Every carrier on DEN to SLC, 7,758 flights

These figures cover 2,329 flights between July 2025 and June 2026. On-time means an arrival less than 15 minutes after the scheduled gate time, the same threshold the Department of Transportation uses in its own reports. Cancelled and diverted flights are excluded from the on-time rate and counted separately, which is why the cancellation column matters on its own.

Carrier by carrier

Southwest against every carrier on DEN to SLC

Southwest flew 2,329 of the 7,758 flights on DEN to SLC, about 30% of it. Its 71.2% on time is 6 points worse than the route as a whole, which runs 77.5%. Ranked by on-time rate it is last of five carriers on the route, where the range runs from Delta at 82.3% to Southwest at 71.2%.

The four carriers here are closely matched: 5 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on DEN to SLC
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	1,689	82.3%	81 min	0.41%	B+
Frontier Airlines	1,010	81.7%	60 min	0.50%	B+
SkyWest Airlines	1,399	79.4%	64 min	0.86%	B+
United Airlines	1,331	77.5%	58 min	0.15%	B+
Southwest Airlines (this page)	2,329	71.2%	52 min	0.47%	C+

No carrier stands out. Delta tops the table at 82.3%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.

Departure window

When Southwest runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 34 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am115 flights81.7%
8am–11am485 flights89.2%
11am–2pm469 flights76.9%
2pm–5pm441 flights71.2%
5pm–8pm356 flights56.2%
8pm–5am463 flights55.7%

Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 55.7% on time, against 89.2% for the 8am–11am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 8am–11am window is the busiest, with 485 flights scheduled in it.

Across the year

Southwest on DEN to SLC through the year

Darker means more delays. Figures are on-time percentages.January best, July worst

July is the worst month at 50.2% on time, 37 points below January, the best at 87.4%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. July was the busiest month here, with 222 flights.

Across the week, Tuesday is the strongest day at 78.1% on time and Sunday the weakest at 66.4%. 12 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Southwest runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 54% of the 35,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
54%
Carrier
37%
National Airspace System
8%
Extreme weather
1%
Security
0%

54% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 35,000 reported delay minutes here, that single category outweighs weather by 54 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 34,746 reported delay minutes.

The largest share of delay minutes, 37%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 13,000 of the 35,000 delay minutes reported here.

Cancellations are rare at 0.47%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

7.4% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 50 minutes, which a normal layover absorbs.

At 391 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 8am–11am window matters as much as it does.

The return leg runs 72.4% on time across 2,328 flights, within about a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

The sample behind these figures is 2,329 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.

What to do with this

Booking Southwest on DEN to SLC

Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 87.4% on time and July 50.2%, a swing of 37 points. If the dates move at all, move them out of July before you think about anything else. 2,316 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures